Cut the sausage into thirds and peel it off. Cut the onions into small cubes and put the butter or butter fat in a pan and let it melt. When the fat starts to sizzle, add the onions and let them brown lightly. Turn a little in between.
When the onions have turned a nice golden brown, cut 3/4 of the cut into the Lyoner and fill in the onions. Place a slice of Gouda or Emmentaler cheese on top of each third of the meat sausage so that the onions do not fall out. Melt the cheese either in the oven at 175 ° C or in the microwave.